1. Field of the Invention
The present invention relates to a surface flaw detecting apparatus of workpiece, and more particularly to a surface flaw detecting apparatus of workpiece disposed, for example, at an exit side of a machine tool for optically detecting or measuring the presence or absence of flaw on the surface of the workpiece while rotating the bar-shaped workpiece after being processed about its axial line.
2. Description of the Related Art
As this type of optical surface flaw detecting apparatus, one comprising a laser sensor composed of a laser oscillator and a photo detector is known. In flaw detecting operation of this surface flaw detecting apparatus, for example as shown in FIG. 10 (a), while rotating a bar-shaped workpiece (hereinafter called work) (W) about its axial line (about 3,000 rpm), and moving a laser sensor (a) gradually in the axial direction of the work (W) (about 25 .mu.m/revolution), the work surface is spirally scanned by the laser sensor (a).
When the axial length of the work W is relatively long, in order to shorten the measuring time, as shown in FIG. 10 (b), a plurality of laser sensors (a) are disposed parallel (three in this example), corresponding to the work length, and they are simultaneously put in action to scan the work surface.
To prevent error in measurement by the laser sensor (a), prior to the measurement, a step to clean the surface of the work (W) is needed. In this type of surface detecting apparatus, for this purpose, an apparatus for a wiping step independent of the measuring step is provided.
In such laser sensor system, however, because of the spiral scanning method as mentioned above, the flaw detecting speed is limited, and if the preceding step of machining is done at high speed, the measuring time per work (W) may become even longer than the machining time. Accordingly, the series of processing steps of the works (W) is stagnant, which may result in increase of line cycle time (machining time+wiping time+measuring time).
For example, when measuring a work (W) of 20 mm in diameter and 300 mm in length by using three laser sensors (a), (a), (a) as shown in FIG. 10 (b), the measuring time takes about 60 seconds. Besides, wiping of the work surface requires another step, and hence the total cycle time is about 80 seconds.
Even in optical measuring method, rotary motion of the work (W) and moving motion of the laser sensor (a) in the work axial direction are mechanical. Accordingly, relating with the spot measurement of the laser sensor (a), a relative deflection is likely to occur between the work (W) and the laser sensor (a), thereby producing a measuring error, and high reliability is not obtained in the measuring precision. In particular, when the rotating speed of the work (W) is increased in order to shorten the measuring time, vibration due to deflection of the work (W) becomes larger, and more measuring errors tend to occur.